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NETIVOT, Israel (CNN) -- Thousands of demonstrators gathered in Netivot Monday singing, praying and chanting in protest against the Israeli government's plan to pull out of Gaza and a small part of the West Bank.

A pro-settler group, The Yesha Council, had predicted between 50,000 and 100,000 people would participate in the demonstration, but Israeli police blocked buses in dozens of Israeli cities as they attempted to ferry riders planning to join the protest.

In a statement, police said, "According to information that has been presented to the Israel Police Commissioner and his senior staff, the organizers and participants of the march plan to violate the law. Therefore, it has been decided to prevent the participants from reaching the area and creating a situation that will disturb the police from carrying out the evacuation."

In 28 days, the Israeli government plans to begin withdrawing all Jewish settlers and Israeli troops from Gaza and four small areas of the northern West Bank.

Israel plans to complete the removal of Jewish settlers and the Israeli troops who guard them from those areas by mid-August.

Last year, Israeli Prime Minister Ariel Sharon announced his country would close 21 settlements and move about 8,000 Israelis from Gaza, which is also home to about 1.3 million Palestinians.

The Yesha Council, which represents Jewish settlers, denounced the action banning its demonstration, saying police were violating the democratic rights of settlers.

The council hadplanned for scores protesters to gather in Netivot with the hope of marching to the Gush Katif block of settlements in southern Gaza.

A Yesha representative said more than 1,000 buses had been hired to carry the demonstrators to the south.

The plan is for the demonstrators to travel to Kfar Maimon, about 10 kilometers to the west where they will spend the night in tents. If police close the roads, the organizers say the event will turn into a march, on roads and through fields.

The goal, according to The Yesha Council, is for the demonstrators to reach Kissufim, the entrance to Gush Katif settlement block, by Wednesday. The Yesha Council hopes the group of demonstrators will be so large Israeli troops and police will not be able to prevent them from joining settlers in Gush Katif to resist the withdrawal.

Israel Defense Forces closed Gaza to everyone but residents and banned the demonstration, saying the Yesha Council had refused to meet the military's demands, the Israeli daily newspaper Haaretz reported.

Israeli police have deployed more than 15,000 troops to the area to control the demonstrators.

Israeli Deputy Prime Minister Ehud Olmert said there are thousands of Israelis who oppose the disengagement because they "simply don't trust the Palestinians."

But he said the Israeli government and Sharon are determined to go forward with the plan in an effort to "create a real opportunity for a change in the Middle East."

He said he hoped that the demonstration will be peaceful and that the protesters will obey the orders of Israeli police and troops in the area.

"I hope it will end up in a civilized manner," he said, adding that if there are deaths or injuries, it will be for the protest organizers to explain.

Olmert repeated the Israeli government's call for the Palestinian Authority to act against Palestinian militant groups such as Hezbollah, Hamas and Islamic Jihad.

He said Palestinian Authority President Mahmoud Abbas is being undermined by his own inaction in dealing with the militant groups.

"It is time for the Palestinians to take measures to stop terror," said Olmert, adding that if the Palestinian Authority acts against terrorists it will be easier for Israel to deal with its demonstrators.